Medicament delivery devices developed for self-administration have become very popular because it allows for the users to provide medicament without the need for visiting a hospital, a clinic or the like in order to receive an injection of medicament.
The devices for self-administration that have been developed contain different degrees of functionality depending e.g. on the application, type of drug and intended user. The different functions may include automatic penetration, injection, mixing, priming, withdrawal from injection site, needle shields, to mention a few.
The majority of injection devices on the market are arranged with elongated, generally tubular medicament containers having one end where an injection needle can be attached, and provided with a movable wall at the other end, such as a rubber stopper. It is further very common to have some sort of elongated driver acting on said stopper, such as a plunger rod. The driver is also often connected to a power source such as compression springs, leaf springs, and the like for urging the plunger rod against the stopper for expelling medicament through the injection needle.
The use of plunger rods is very well developed and they be moved forward by the power source either linearly or rotatingly. A general desire from many users is to have as small devices as possible in order that they shall not attract too much attention, especially when the devices sometimes are to be used in the public. A problem with the above mentioned use of plunger rods is that the device has to be at least somewhat longer than the length of the medicament container plus the length of the plunger rod. The length problem becomes even more pronounced when functionality is added to the injector, such as dose setting buttons, needle shields extending from the injector, to mention some. The problem is also more pronounced the longer the plunger has to move inside the medicament container, either that the doses are large or that the injector is designed to deliver a number of doses before the container is emptied.
A few attempts have been made to solve this problem. One such solution is shown in document U.S. Pat. No. 6,641,566 where the power source is placed parallel to the medicament container. Here the plunger rod is designed flexibly bendable around a wheel in order that the power source can act on the container via the plunger rod. However, even if the device becomes shorter, by necessity it becomes thicker and also obtains a shape that is more difficult to hold for a user. This means that the device is not as discrete as desired. Further, many patients have by now gotten used to injectors having a general pen-shape and are thus reluctant to adapt to other shapes.
Another solution is shown in EP 1 647 292 A1 wherein the activation mechanism requires a rather complex design.
There is thus room for improvement regarding the size and design of injector.